Odbms concepts

ADBMS
By:
Dabbal S. Mahara
2018

Traditional Data Models
 Traditional Data Models:
• Hierarchical
• Network (since mid-60’s)
• Relational (since 1970 and commercially since 1982)
 These traditional models have been quite successful in
developing the database technology required for many
traditional business database applications.
2

RELATIONAL MODEL
 Relations are the key concept, everything else is around relations
 Primitive data types, e.g., strings, integer, date, etc.
 Great normalization, query optimization, and theory
 What is missing?
• Handling of complex objects
• Handling of complex data types
• Code is not coupled with data
• No inheritance, encapsulation, etc.
3

Object-Oriented Database
 Relational model has certain limitations when more complex database
applications must be designed and implemented, like CAD/CAM, CIM,
scientific experiments, telecommunications, GIS, and multimedia.
 Object Oriented (OO) Data Models since mid-90’s, to address the
limitations of traditional relational database models.
 The key feature of object-oriented databases is the power they give the
designer to specify both the structure of complex objects and the
operations that can be applied to these objects.
4

Why Object-Oriented Databases?
 Reasons for creation of Object Oriented Databases
• Need for more complex applications
• Need for additional data modeling features
• Increased use of object-oriented programming languages
 Commercial OO Database products –
• Several in the 1990’s, but did not make much impact on
mainstream data management
5

Object-Orientation Concepts
 Class
 Object
 Abstraction
 Encapsulation
 Interface
 Methods and their Signatures
 Attributes
 Object State
6

History of OO Models and Systems
 Languages:
 Simula (1960’s)
 Smalltalk (1970’s)
 C++ (late 1980’s)
 Java (1990’s and 2000’s)
7

(contd.)
 Experimental Systems:
• Orion at MCC (Microelectronics and Computer
Technology Corporation) in Austin.
• IRIS at H-P labs
• Open-OODB at T.I.
• ODE at ATT Bell labs
• Postgres - Montage - Illustra at UC/B
• Encore/ObServer at Brown
8

(contd.)
 Commercial OO Database products:
• Ontos
• Gemstone
• O2
• Objectivity
• Objectstore
• Versant
• Poet
• Jasmine (Fujitsu – GM)
9

 ODBMS is a database management system that implements
object-oriented data model
 The Object-oriented Database System Manifesto, Atkinson et
all, 1989. – in scientific paper described the properties which
ODBMS must satisfy:
• Object-oriented concepts
• Database management system concepts
 Implementation of object-oriented database management system
(ODBMS) is generally programmed for a specific programming language,
and differ quite with each other.
10Object-Oriented Database

Limitations of ODBMS
 No logical data independence : Modifications to the database (schema
evolution) require changes to the application and vice versa
 Lack of agreed standards, the existing standard (ODMG) is not fully
implemented
 Dependence on a single programming language. Typical OODBMS is
tied to a single programming language with it's programming interface
 Lack of interoperability with a large number of tools and features that
are used in SQL
 Lack of Ad-Hoc queries (queries on the new tables that are obtained
by joining new tables with the existing ones)
11

ODBMS in real world
 Chicago Stock Exchange - management in stocks trade (Versant)
 Radio Computing Services – automation of radio stations (POET)
 Ajou University Medical Canter in South Korea – all functions of the
hospital, including those critical such as pathology, laboratory,
blood bank, pharmacy and radiology
 CERN – big scientific data sets (Objectivity/DB)
 Federal Aviation Authority – simulation of passengers and baggage
 Electricite de France – management in electric power networks
12

What is Object-Oriented Data Model?
 OO databases try to maintain a direct correspondence between
real-world and database objects so that objects do not lose their
integrity and identity and can easily be identified and operated
upon.
 Relations are not the central concept, classes and objects are the
main concept.
 Main Features:
• Powerful type system
• Classes
• Object Identity
• Inheritance
15

FEATURE 1: POWERFUL TYPE SYSTEM
 Primitive types : Integer, string, date, Boolean, float, etc.
 Structure type : Attribute can be a record with a schema,
struct { integer x, string y}
 Collection type : Attribute can be a Set, Bag, List, Array of
other types
 Reference type: Attribute can be a Pointer to another object
 OODBMS are capable of storing complex objects, I.e., objects
that are composed of other objects, and/or multi-valued
attributes.
16

FEATURE 2: CLASSES
 A ‘class’ is in replacement of ‘relation’
 Same concept as in OO programming languages
• All objects belonging to a same class share the same properties and behavior
 An ‘object’ can be thought of as ‘tuple’ (but richer content)
 An object is made of two things:
• State: attributes (name, address, birthDate of a person)
• Behavior: operations (age of a person is computed from birthDate and
current date)
 Classes encapsulate data + methods + relationships
• Unlike relations that contain data only
 In OODBMSs objects are persistent (unlike OO programming languages)
17

FEATURE 3: OBJECT IDENTITY
 OID is a unique, unchangeable object identifier generated
by the OO system regardless of its content
 Independent of the values of the object attributes
 Invisible to the user
 Used for referencing objects
 Two objects are identical if they have the same identity of
the object - property that uniquely identifies them
 Even if all attributes are the same, still objects have
different OIDs
18

FEATURE 4: INHERITANCE
 A class can be defined in terms of
another one.
 Person is super-class and Student is
sub-class.
 Student class inherits attributes and
operations of Person.
19

Encapsulation
 Related to the concepts of abstract data types and information hiding in
programming languages
 The encapsulation is achieved through objects and its operations.
 Some OO models insist that all operations a user can apply to an object
must be predefined. This forces a complete encapsulation of objects.
 To encourage encapsulation, an operation is defined in two parts:
• signature or interface of the operation, specifies the operation name
and arguments (or parameters).
• method or body, specifies the implementation of the operation.
20

Encapsulation
 Operations can be invoked by passing a message to an
object, which includes the operation name and the
parameters. The object then executes the method for that
operation.
 This encapsulation permits modification of the internal
structure of an object, as well as the implementation of its
operations, without the need to disturb the external
programs that invoke these operations.
21

Polymorphism
 This refers to an operation’s ability to be applied to different types of
objects; in such a situation, an operation name may refer to several
distinct implementations, depending on the type of objects it is applied
to.
 Operator overloading: It allows the same operator name or symbol to be
bound to two or more different implementations of the operator,
depending on the type of objects to which the operator is applied
 For example + can be:
Addition in integers
Concatenation in strings (of characters)
22

Object Structure
 Every instance of an object is characterized by its state.
 Structure of an object instance is represented by a triple: (i,
c, v)
where i : object identifier
c : type constructor
v : object state or value
23

Type Constructors
 In OO databases, the state (current value) of a complex object
may be constructed from other objects (or other values) by using
certain type constructors.
 The three most basic constructors are atom, tuple and set.
 Other commonly used constructors include list, bag, and array.
 The atom constructor is used to represent all basic atomic
values, such as integers, real numbers, character strings,
Booleans, and any other basic data types that the system
supports directly.
24

Type Constructors
 The tuple type constructor is often called a structured type,
since corresponds to struct construct in C and C++. It
represents a tuple of the form <a1:i1, a2:i2,..., an:in> where aj is
attribute name and each ij is an OID.
 The set type constructor represents a set of OIDs { i1,i2,...,in},
which are the OIDs of objects of typically of same type.
 List type constructor represent the ordered list of OIDs of the
same type.
25

 Array type constructor is single dimension array of
OIDs.
 The main difference between list and array is that a
list can have an arbitrary number of element whereas
the array has a maximum size.
 The bag is similar same as set but bag has duplicate
elements.
26
Type Constructors

Object Identity, Object Structure, and
Type Constructors
 Example 1
 One possible relational database state corresponding to COMPANY
schema
27

Object Identity, Object Structure, and Type
Constructors
 Example 1 (contd.):
28

Constructors
 Example 1 (contd.)
29

Constructors
We use i1, i2, i3, . . . to stand for unique system-generated object
identifiers. Consider the following objects:
 o1 = (i1, atom, ‘Houston’)
 o2 = (i2, atom, ‘Bellaire’)
 o3 = (i3, atom, ‘Sugarland’)
 o4 = (i4, atom, 5)
 o5 = (i5, atom, ‘Research’)
 o6 = (i6, atom, ‘1988-05-22’)
 o7 = (i7, set, {i1, i2, i3})
30

Type Constructors
 Example 1(contd.)
 o8 = (i8, tuple, <dname:i5, dnumber:i4, mgr:i9, locations:i7,
employees:i10, projects:i11>)
 o9 = (i9, tuple, <manager:i12, manager_start_date:i6>)
 o10 = (i10, set, {i12, i13, i14})
 o11 = (i11, set {i15, i16, i17})
 o12 = (i12, tuple, <fname:i18, minit:i19, lname:i20, ssn:i21, . . ., salary:i26,
supervisor:i27, dept:i8>)
 . . .
31

Type Constructors
 The first six objects listed in this example represent atomic
values.
 Object seven is a set-valued object that represents the set
of locations for department 5; the set refers to the atomic
objects with values {‘Houston’, ‘Bellaire’, ‘Sugarland’}.
 Object 8 is a tuple-valued object that represents
department 5 itself, and has the attributes DNAME,
DNUMBER, MGR, LOCATIONS, and so on.
32

Type Constructors
 Example 2:
 This example illustrates the difference between the two
definitions for comparing object states for equality.
 o1 = (i1, tuple, <a1:i4, a2:i6>)
 o2 = (i2, tuple, <a1:i5, a2:i6>)
 o3 = (i3, tuple, <a1:i4, a2:i6>)
 o4 = (i4, atom, 10)
 o5 = (i5, atom, 10)
 o6 = (i6, atom, 20)
33

Constructors
 Example 2 (contd.):
 In this example, The objects o1 and o2 have equal states,
since their states at the atomic level are the same but the
values are reached through distinct objects o4 and o5.
 However, the states of objects o1 and o3 are identical,
even though the objects themselves are not because they
have distinct OIDs.
 Similarly, although the states of o4 and o5 are identical,
the actual objects o4 and o5 are equal but not identical,
because they have distinct OIDs.
34

Object Identity,
Object Structure,
and Type
Constructors
35
Figure
Representation of a
DEPARTMENT complex
object as a graph

Object Structure and Type Constructors
36

Specifying Object Behavior via Class
Operations
The main idea is to define the behavior of a type of
object based on the operations that can be externally
applied to objects of that type.
In general, the implementation of an operation can be
specified in a general-purpose programming language
that provides flexibility and power in defining the
operations.
37

Specifying Object Behavior via Class
Operations (contd.):
 For database applications, the requirement that all objects be
completely encapsulated is too stringent.
 One way of relaxing this requirement is to divide the structure of
an object into visible and hidden attributes (instance variables).
 The visible attributes may be directly accessed for reading by
external operators of by high level query language.
 The hidden attributes of an object are completely encapsulated
and can be accessed only through predefined operations.
38

Encapsulation of
Operations
39

Persistence of Objects
 Persistent objects are the objects that are created and stored in
database and exist even after the program termination.
 Typical mechanisms for making an object persistence are:
Naming and Reachability.
• Naming Mechanism: Assign an object a unique persistent
name through which it can be retrieved by this and other
programs.
• Reachability Mechanism: Make the object reachable from
some persistent object. An object B is said to be reachable
from an object A if a sequence of references in the object
graph lead from object A to object B.
40

Inheritance
 Type (class) Hierarchy
• A type in its simplest form can be defined by giving it a type
name and then listing the names of its visible (public) functions
• When specifying a type in this section, we use the following
format, which does not specify arguments of functions, to
simplify the discussion:
• TYPE_NAME: function, function, . . . , function
• Example:
PERSON: Name, Address, Birthdate, Age, SSN
41

Inheritance
 Subtype:
When the designer or user must create a new type that is
similar but not identical to an already defined type Supertype.
Subtype inherits all the functions of the Supertype.
Example: 1
• PERSON: Name, Address, Birthdate, Age, SSN
• EMPLOYEE subtype-of PERSON: Salary, HireDate, Seniority
• STUDENT subtype-of PERSON: Major, GPA
42

Inheritance: Example (2)
 Consider a type that describes objects in plane geometry, which may
be defined as follows:
• GEOMETRY_OBJECT: Shape, Area, ReferencePoint
 Now suppose that we want to define a number of subtypes for the
GEOMETRY_OBJECT type, as follows:
• RECTANGLE subtype-of GEOMETRY_OBJECT: Width, Height
• TRIANGLE subtype-of GEOMETRY_OBJECT: Side1, Side2, Angle
• CIRCLE subtype-of GEOMETRY_OBJECT: Radius
43

Inheritance: Example (2) (contd.)
 An alternative way of declaring these three subtypes is to specify
the value of the Shape attribute as a condition that must be
satisfied for objects of each subtype:
• RECTANGLE subtype-of GEOMETRY_OBJECT (Shape=‘rectangle’):
Width, Height
• TRIANGLE subtype-of GEOMETRY_OBJECT (Shape=‘triangle’): Side1,
Side2, Angle
• CIRCLE subtype-of GEOMETRY_OBJECT (Shape=‘circle’): Radius
44

Inheritance
 Multiple Inheritance and Selective Inheritance
Multiple inheritance in a type hierarchy occurs when a
certain subtype T is a subtype of two (or more) types and
hence inherits the functions (attributes and methods) of
both supertypes.
For example, we may create a subtype
ENGINEERING_MANAGER that is a subtype of both
MANAGER and ENGINEER.
This leads to the creation of a type lattice rather than a type
hierarchy.
45

Extents
 Extents:
 The collection of objects of the same type in the database is known as
an extent of the type.
 Extent is the current set of objects belonging to the class.
 Queries in OQL refer to the extent of a class and not the class directly.
 Persistent Collection:
 This holds a collection of objects that is stored permanently in the
database and hence can be accessed and shared by multiple
programs
 Transient Collection:
 This exists temporarily during the execution of a program but is not kept
when the program terminates
46

Complex Objects
Unstructured complex object:
 These is provided by a DBMS and permits the storage and retrieval
of large objects that are needed by the database application.
 Typical examples of such objects are bitmap images and long
text strings (such as documents); they are also known as binary
large objects, or BLOBs for short.
 This has been the standard way by which Relational DBMSs
have dealt with supporting complex objects, leaving the
operations on those objects outside the RDBMS.
47

Complex Objects
 Structured complex object:
 This differs from an unstructured complex object in that the object’s
structure is defined by repeated application of the type constructors
provided by the OODBMS.
 Hence, the object structure is defined and known to the OODBMS.
 The OODBMS also defines methods or operations on it.
 For example: The DEPARTMENT object is structured object.
48
define type DEPARTMENT
tuple ( Dname: string;
Dnumber: integer;
Mgr: tuple ( Manager: EMPLOYEE;
Start_date: DATE; );
Locations: set(string);
Employees: set(EMPLOYEE);
Projects: set(PROJECT); );

Versions and Configurations
 Versions
• Some OO systems provide capabilities for dealing with multiple
versions of the same object (a feature that is essential in design and
engineering applications).
• For example, an old version of an object that represents a tested
and verified design should be retained until the new version is tested
and verified: very crucial for designs in manufacturing process
control, architecture , software systems …..
 Configuration:
• A configuration of the complex object is a collection consisting of
one version of each module arranged in such a way that the module
versions in the configuration are compatible and together form a
valid version of the complex object.
49

Current Status
 OODB market growing very slowly these days.
 O-O ideas are being used in a large number of applications, without
explicitly using the OODB platform to store data.
 Growth:
 O-O tools for modeling and analysis, O-O Programming
Languages like Java and C++
 Compromise Solution Proposed:
 Object Relational DB Management (Informix Universal Server,
Oracle 11g, IBM’s UDB, DB2/II …)
50

Exercise
51
1. What is OID? How persistent objects are maintained in OO Database?
2. Define state of an object. Distinguish between persistent and transient
objects.
3. Distinguish multiple inheritance and selective inheritance in OO
concepts.
4. What is the difference between structured and unstructured complex
object? Differentiate identical versus equal objects with examples.
5. What are the advantages and disadvantages of OODBMS?

Odbms concepts

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